1. Field of the Invention
The present invention relates in general to an ink jet print head and method of manufacturing the same, and more particularly, to an ink jet print head which has a novel structure that assures improved and stable ink-jetting characteristics or capability, and which is available at a reduced cost. The ink jet print head according to the present invention includes piezoelectric/electrostrictive elements provided in pressure chambers communicated with nozzle openings which compress the ink pressure chambers to form ink droplets. The ink jet print head is formed by arranging a nozzle plate, ink pressure chamber forming members and a vibrating plate on one another.
2. Discussion of the Prior Art
In the recent market of printers used as output devices of computers and the like, there is a rapidly increasing demand for an ink jet printer which operates quietly at relatively low cost. The ink jet printer includes an ink jet print head which is generally adapted to raise the pressure in an ink chamber filled with a mass of ink, to thereby jet or discharge fine ink particles of ink from nozzles so as to effect printing.
There is known one type of the ink jet print head which has piezoelectric/electrostrictive elements respectively disposed on a wall of the ink pressure chambers, as means for raising the pressure in the ink pressure chambers as described above. More particularly, piezoelectric/electrostrictive elements, such as piezoelectric transducers, are coupled to diaphragms which form walls of respective ink pressure chambers, wherein displacement of the piezoelectric transducers varies the volume of the ink pressure chambers to thereby eject ink droplets. In this type of printhead, a volume of the ink pressure chamber is changed upon energization and displacement of the piezoelectric transducers.
The ink jet print head of this type is advantageous in reduced consumption of electric power, as compared with another type of ink jet print head which is adapted to heat the ink by a heater disposed in the ink chamber, to generate minute bubbles used for jetting the fine ink particles. The above-described ink jet print head is also advantageous in that, since the displacement of the diaphragms by the piezoelectric transducers takes place over a relatively large area of the ink pressure chambers, ink droplets can be formed stably.
FIGS. 5 and 6 illustrate an example of the above type of ink jet print head. A metallic nozzle plate 4 having a plurality of nozzles 2, a metallic orifice plate 8 having plurality of orifices 6, and a channel plate 10 are superposed on each other such that the channel plate 10 is interposed between the plates 4, 8, and these plates 4, 8, 10 are bonded together into an flow path unit 16. In this flow path unit 16, there are formed a plurality of ink discharge channels 12 for leading or guiding an ink material to the respective nozzles 2, and at least one ink supply channel 14 for leading or supplying the ink material to the orifices 6.
The ink jet print head further includes a pressure generating unit 24 which consists of two plates 18, 20 made of metal or synthetic resin and formed in lamination on the flow path unit 16. The pressure generating unit 24 has a plurality of voids 22 which correspond to the nozzles 2 and orifices 6. With this pressure generating unit 24 superposed on and bonded to the flow path unit 16, each of the voids 22 provides an ink pressure chamber 26 formed behind the corresponding nozzle and orifice 2, 6. The ink jet print head also includes a plurality of piezoelectric/electrons respective elements 28, such as piezoelectric transducers, each of which is secured to a wall of the corresponding ink pressure chamber 26 remote from the flow path unit 16.
In producing the above type of ink jet print head, however, small pieces of the piezoelectric/electrostrictive elements 28 must be bonded to the walls of the respective ink pressure chambers 26, which makes it extremely difficult to render the resulting print head sufficiently small-sized. Further, the bonding of the piezoelectric/electrostrictive elements 28 inevitably pushes up the cost of manufacture of the print head, and makes it difficult for the elements 28 to maintain sufficiently high reliability.
In the production of the above-described ink jet print head, another problem arises when the flow path unit 16 and pressure generating unit 24 are bonded together. Namely, the spacing between the adjacent voids 22, 22 formed in the print head, that is, the thickness "t" of a partition wall 30 which separates the adjacent voids from each other, is considerably small, ore precisely, about 1 mm or smaller. Such a small spacing between the voids 22 makes it extremely difficult to bond the flow path unit 16 and the pressure generating unit 24 to each other.
More specifically, an adhesive used for bonding the flow path unit 16 and the pressure generating unit 24 is likely to overflow onto the opposite surfaces of the partition wall 30. Therefore, the ink pressure chambers 26 and/or ink flow channels including the ink supply and discharge channels 12, 14 and orifices 6 may be deformed, whereby the ink-jetting characteristics of the print head may deteriorate, resulting in reduced quality and yield of the products print heads).
If the amount of the adhesive applied is reduced to avoid its overflow as described above, it is likely that the flow path unit 16 and pressure generating unit 24 are insufficiently or poorly bonded together at some portions of the interface of the members 16, 24. This may result in incomplete sealing between the adjacent ink pressure chambers 26, 26, causing leakage of the pressures of the ink pressure chambers 26, 26 and consequent crosstalk for example. The partial or insufficient bonding may also leave gaps between the bonding surfaces of the units 16, 24, resulting in pressure loss upon pressurizing of the ink pressure chambers 26 due to the air remaining the gaps. Consequently, the ink-jetting characteristics of the print head may be lowered.
In the ink jet type print head disclosed in Japanese Unexamined Patent Publication No. Sho. 62-111758, pressure generating members including diaphragms and flow path forming members are formed in a layered construction, and nozzle openings are provided in a row extending parallel to the direction of displacement of the diaphragm, thereby to reduce the thickness of the print head. That is, the print head has a layered structure.
The layered structure is advantageous in that the print head can be miniaturized, and it can be manufactured using a simple method for joining plate members formed by pressing or etching.
In the manufacturing method for producing the print head, an adhesive agent is used for joining the plate members. However, during manufacture, as noted above, the adhesive agent can sometimes flow into small holes which form ink flow paths in the plate members, thus changing the ink flow resistance thereof, lowering the reliability in operation of the print head. Furthermore, because the piezoelectric/electrostrictive elements must be fixed to the diaphragm with an adhesive agent or by etching or laser welding, the manufacture of the print head requires much time and labor.
In order to eliminate the above-described difficulties, an ink it type print head has been proposed, for example, in Japanese Unexamined Patent Publication No. Sho. 63-149159, which is formed by layering ceramic plates in a semi-solid state, shaped as require to form flow path members, and piezoelectric transducers, one on another and subjecting the structure to firing. That is, the print head is manufactured without a separate step of mounting the piezoelectric transducers. However, the method is still disadvantageous in that it cannot achieve a reduction in the thickness of the print head since the nozzle openings extend in a direction perpendicular to the direction of displacement of the diaphragm.